Research is being conducted on factors affecting puberty in female mammals, and house mice in particular. Genetic selection for early and late first estrus produced two stocks of mice, one maturing at 28 days of age and the other at 44 days of age (base stock females mature at 35 days). Further experiments revealed that these selected mice still retained some flexibility in age of maturation; social and chemosignal factors sped up puberty in slow stocks and delayed puberty in fast stock females. Reversal selection is currently in progress and a selection study on wild Mus will begin shortly. A second line of investigations tested the various methods which have been utilized to provide young females with urinary chemosignals. The male cue which accelerates puberty is apparently received via the vomeronasal organ whereas the puberty-delaying cue in urine from grouped females is received by the olfactory epithelium. Other studies have explored the effects of different doses of urinary chemosignals and mixing of urine from different sources. These experiments are potentially significant in terms of our understanding of rodent population regulation, the mechanisms of production and effect for chemosignals in mammals and the flexibility of and factors affecting sexual maturation in mammals, including man.